Current eukaryotic vector technologies can be divided into two basic categories, viral and non-viral vectors. Viral vectors tend to be much more efficient in terms of delivery, maintenance and overall expression levels. They suffer, however, from the need to be infective, which raises obvious safety concerns and implicates complicated processing technologies, like packaging systems and helper viruses.
Non-viral systems are considered more desirable because of their more defined characteristics, but the suffer from delivery and stability problems. One such problem is that typical delivery systems do not efficiently provide the vector in the nuclear context, where it is best maintained and expressed.
It is desirable, therefore, to develop a vector system that efficiently mediates transfer from the cytoplasm to the nucleus, where more efficient gene expression is possible. Moreover, it is desirable to provide a stable episomal vector that has a higher copy number than the chromosome.